/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         https://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
#ifndef itkHessian3DToVesselnessMeasureImageFilter_hxx
#define itkHessian3DToVesselnessMeasureImageFilter_hxx

#include "itkImageRegionIterator.h"
#include "itkMath.h"

namespace itk
{

template <typename TPixel>
Hessian3DToVesselnessMeasureImageFilter<TPixel>::Hessian3DToVesselnessMeasureImageFilter()
{
  m_Alpha1 = 0.5;
  m_Alpha2 = 2.0;

  // Hessian( Image ) = Jacobian( Gradient ( Image ) )  is symmetric
  m_SymmetricEigenValueFilter = EigenAnalysisFilterType::New();
  m_SymmetricEigenValueFilter->OrderEigenValuesBy(EigenValueOrderEnum::OrderByValue);
}

template <typename TPixel>
void
Hessian3DToVesselnessMeasureImageFilter<TPixel>::GenerateData()
{
  itkDebugMacro("Hessian3DToVesselnessMeasureImageFilter generating data ");

  m_SymmetricEigenValueFilter->SetInput(this->GetInput());

  typename OutputImageType::Pointer output = this->GetOutput();

  using EigenValueOutputImageType = typename EigenAnalysisFilterType::OutputImageType;

  m_SymmetricEigenValueFilter->Update();

  const typename EigenValueOutputImageType::ConstPointer eigenImage = m_SymmetricEigenValueFilter->GetOutput();

  // walk the region of eigen values and get the vesselness measure
  EigenValueArrayType                                 eigenValue;
  ImageRegionConstIterator<EigenValueOutputImageType> it;
  it = ImageRegionConstIterator<EigenValueOutputImageType>(eigenImage, eigenImage->GetRequestedRegion());
  ImageRegionIterator<OutputImageType> oit;
  this->AllocateOutputs();
  oit = ImageRegionIterator<OutputImageType>(output, output->GetRequestedRegion());
  while (!it.IsAtEnd())
  {
    // Get the eigen value
    eigenValue = it.Get();

    // normalizeValue <= 0 for bright line structures
    double normalizeValue = std::min(-1.0 * eigenValue[1], -1.0 * eigenValue[0]);

    // Similarity measure to a line structure
    if (normalizeValue > 0)
    {
      double lineMeasure;
      if (eigenValue[2] <= 0)
      {
        lineMeasure = std::exp(-0.5 * itk::Math::sqr(eigenValue[2] / (m_Alpha1 * normalizeValue)));
      }
      else
      {
        lineMeasure = std::exp(-0.5 * itk::Math::sqr(eigenValue[2] / (m_Alpha2 * normalizeValue)));
      }

      lineMeasure *= normalizeValue;
      oit.Set(static_cast<OutputPixelType>(lineMeasure));
    }
    else
    {
      oit.Set(NumericTraits<OutputPixelType>::ZeroValue());
    }

    ++it;
    ++oit;
  }
}

template <typename TPixel>
void
Hessian3DToVesselnessMeasureImageFilter<TPixel>::PrintSelf(std::ostream & os, Indent indent) const
{
  Superclass::PrintSelf(os, indent);

  os << indent << "Alpha1: " << m_Alpha1 << std::endl;
  os << indent << "Alpha2: " << m_Alpha2 << std::endl;
}
} // end namespace itk

#endif
